There are many examples of radio communications systems in which data is communicated using Orthogonal Frequency Division Multiplexing (OFDM). Television systems which have been arranged to operate in accordance with Digital Video Broadcasting (DVB) standards for example, use OFDM for terrestrial and cable transmissions. OFDM can be generally described as providing K narrow band sub-carriers (where K is an integer) which are modulated in parallel, each sub-carrier communicating a modulated data symbol such as for example Quadrature Amplitude Modulated (QAM) symbol or Quaternary Phase-shift Keying (QPSK) symbol. The modulation of the sub-carriers formed in the frequency domain and transformed into the time domain for transmission. Since the data symbols are communicated in parallel on the sub-carriers, the same modulated symbols may be communicated on each sub-carrier for an extended period. The sub-carriers are modulated in parallel contemporaneously, so that in combination the modulated carriers form an OFDM symbol. The OFDM symbol therefore comprises a plurality of sub-carriers each of which has been modulated contemporaneously with different modulation symbols. During transmission, a guard interval filled by a cyclic prefix of the OFDM symbol precedes each OFDM symbol. When present, the guard interval is dimensioned to absorb any echoes of the transmitted signal that may arise from multipath propagation.
It has been proposed for a television system known as the Advanced Television Systems Committee (ATSC) 3.0 in a publication entitled ATSC 3.0 Working Draft System Discovery and Signaling [1] to include a preamble in a transmitted television signal which is carrying broadcast digital television programmes. The preamble includes a so called “bootstrap” signal which is intended to provide a receiver with a part of the transmitted signal which can have a greater likelihood of detecting and therefore can serve as a signal for initial detection. This is because broadcasters anticipate providing multiple services, within a broadcast signal in addition to just broadcast television.
However, in ISDB-T, a present standard for broadcast networks that employ OFDM where services are time-division multiplexed (TDM) together in a single channel, a problem exists in that once the tuner has been set, capacity for mobile services is limited. Given the increasing demand for mobile television, such a problem is becoming increasingly pertinent.
It is proposed that for the next standard, ISDB-T3, a frame structure is designed which can be configured for either frequency division multiplexing (FDM) or TDM. Such a frame structure is proposed herein, and defined with regard to embodiments of the present technique.